1. Technical Field
The present invention relates to an actuator that drives an object such as a mirror, an optical device having the actuator, and a method for manufacturing the actuator.
2. Related Art
For a microelectro mechanical system (MEMS) device, a mirror device is used, for example. To rotate this device, it is necessary to use an actuator. For an actuator of this kind, a parallel flat plate actuator and an electromagnetic actuator have been used. However, the parallel flat plate actuator has a disadvantage in that the drive torque becomes very small when the movable plate is set apart from the electrode plate and that not enough deflection angle can be obtained when the movable plate and the electrode plate are set close to each other in order to increase the drive torque.
Regarding the electromagnetic actuator, although the drive force is large, there is a disadvantage in that it requires wires to flow electric current to the structure, that heat is generated due to the flow of current, and that the device size increases since a permanent magnet is provided therewith.
As a substitution for such actuators, a perpendicular comb-tooth actuator is recently receiving attention. The perpendicular comb-tooth actuator is an electrostatic attraction type actuator as is the parallel flat plate actuator. However, because the perpendicular comb-tooth actuator can have a high driving torque, have no restriction on the deflection angle, have a much simpler structure than that of the electromagnetic actuator, and is thus easier to manufacture, a number of research developments and reports have been made on the MEMS device equipped with the perpendicular comb-tooth actuator. For example, JP-A-2004-301865 (p. 1, FIGS. 1 and 2) proposes this type of an actuator.
However, the actuator depicted in the referenced document has the following problem. That is, when a movable comb-teeth shaped structure is coupled to a plus side and a fixed comb-teeth shaped structure is coupled to a minus side to give a potential difference between the two, the movable comb-teeth shaped structure is attracted to the fixed comb-teeth shaped structure by electrostatic attraction. This generates a torsional moment on the torsion bar, and the movable plate produces a displacement angle against the support substrate. Because it is simply that the plus voltage is applied to the movable comb-teeth shaped structure and the minus voltage is applied to the fixed comb-teeth shaped structure, the drive force for driving the movable plate cannot be arbitrarily adjusted, and, thus, the movable plate cannot be freely controlled.